The present invention relates to a nickel (Ni)-based corrosion-resistant alloy to be used for build-up welding (or cladding) a metallic base in various machine parts such as the cylinder bores of internal combustion engines for automobiles and, more particularly, to a nickel-based corrosion-resistance alloy for build-up welding, which contains not only copper (Cu) and molybdenum (Mo) added to improve its corrosion resistance to acids but also silicon (Si) and boron (B) added to give self-fluxing properties.
Materials for the cylinder bores of automotive engines, especially Diesel engines are required to have not only heat and wear resistances but also excellent corrosion resistance. This requirement invokes the use of the nickel-based alloy. Since, however, the nickel per se is an expensive metal, it has been conceived to form the cylinder bore by build-up welding the nickel-based alloy to a base made of cast iron, steel or aluminum (Al) alloy. The cylinder bore of a Diesel engine has to be well resistant to acids because it is used under the corrosive circumstances of acids. This necessity cannot be sufficiently met by the ordinary nickel-based alloy of the prior art.
Meanwhile, copper and molybdenum has been added in the prior art to the nickel-based alloy so as to improve the corrosion resistance especially to acids. In Japanese Patent Publication No. 56-52982, for example, there is disclosed a nickel-based austenite of high chromium (Cr) and iron (Fe) contents, which contains 30 to 48% of Ni, 30 to 35% of Cu, 3 to 25% of Fe, 1 to 0.5% of manganese (Mn), 4 to 7.5% of cobalt (Co), 0.05 to 0.25% of carbon (C), less than 4% of Si, 2.5 to 8% of Cu and less than 3% of Mo (wherein Mo+Si is less than 4%). This alloy is vaunted by the disclosure to have excellent corrosion resistance, hardenability and malleability. Another Japanese Patent Laid-Open No. 50-75518 has disclosed an alloy which is composed mainly of Ni and Cr blended with smaller amounts of Mo, Cu and another alloy element (and which is exemplified by the composition of 63.0% of Ni, 12.0% of Cr, 5.0% of Cu, 3.0% of Mo, 3.0% of tin (Sn), 3.0% of bismuth (Bi), 1.0% of Si and 1.0% of Mn, the remainder being Fe). This alloy is also vaunted to have excellent corrosion and galling resistances. Another commercially available Ni-based alloy is known as either the "Hastelloy (registered under the trade mark) G alloy" which contains 1.5 to 2.5% of Cu and 5.5 to 7.5% of Mo or the "Hastelloy (registered under the trade mark) G-3 alloy" which contains 1.5 to 2.5% of Cu and 6.0 to 8.0% of Mo.
The above-specified Cu- and Mo-added type Ni-based alloy of the prior art is designed not as the alloy for build-up welding but as an ordinary extendible material, stressing the ductility and hot workability. The amounts of Cu and Mo added are within a range not to deteriorate or to improve the ductility and hot workability. In case those alloys of the prior art are used for the build-up welding of the surface of a metallic base so as to improve the corrosion resistance locally, they will be subject to troubles of bead cracks. In the case of the build-up welding to improve the corrosion resistance, moreover, the alloys are desired to have the so-called "self-fluxing" properties, in which the alloys will flux autogenously to form satisfactory slug, so as to reduce the pin holes or oxide intermediates in the cladding. This desire cannot be satisfied by the above-specified alloys of the prior art because of their insufficient self-fluxing properties.